1. Field of the Invention
The present invention relates to a bar code reader using holograms for reading the bar code of a bar code label attached to each of the goods to be monitored.
2. Description of the Prior Art
Various bar code readers are known as disclosed in Japanese Patent Publication No. 61-53757, for example. In the disclosed bar code reader, diffracting action of holograms is utilized to route a laser beam in a scanning pattern for scanning the bar code of a bar code label. Light reflected from the thus scanned bar code is collected by again utilizing the diffracting action of the holograms, and the collected reflected light is then detected to read the information on the bar code of the bar code label.
With the known bar code reader thus constructed, the scanning laser beam directed to the holograms advances along one path and the reflected light returning back from the holograms advances along the same path. Consequently, it occurs likely that unwanted light generated toward the incident side of the holograms, that is, scattered light or unwanted diffracted light caused by the diffracting action of the holograms advances toward a detector along the path of the reflected light and then detected by the detector as an optical noise, thereby deteriorate the reading accuracy of the bar code reader. This problem becomes significant when the distance between the detector and a bar code to be read is relatively long and light reflected from the bar code is weak.
One solution to the foregoing problem is proposed in Japanese Patent Publication No. 59-22992 wherein an absorption pipe is provided to absorb or otherwise cut light reflected from holograms acting as a scanner. Since the holograms having a light-collecting function are used also as a condenser lens, light incident upon the holograms must be divergent light. Accordingly, if a collimated or parallel beam of light such as a laser beam is used ad the incident light, then an adjustment is needed to convert the laser beam to the divergent light.